Dissimilar Write Prioritization in ZNS Devices

ABSTRACT

The present disclosure generally relates to creating new zones in a data storage device in a manner that ensures substantially even workload of the memory device storage locations. When receiving a zone open command in a zone namespace (ZNS) system, rather than randomly selecting an unopen zone, zones may be categorized based upon storage location workload so that any new zone that is opened utilizes the least utilized storage location. In so doing, generally even workload of the memory device storage locations is achieved.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

Embodiments of the present disclosure generally relate to efficient utilization of dies in a zone namespace (ZNS) device.

Description of the Related Art

In data storage devices, logical blocks are formed across physical blocks to increase the hardware (HW) workload efficiency during sequential performances. In ZNS devices, the logical blocks are not formed across an entire set of dies, but rather, a logical zone itself could be a single physical block or a few physical blocks, unlike full-fledged interleaving. Multiple such smaller logical blocks constitute a zoned namespace within the ZNS device. The zoned namespaces in a ZNS device is helpful for data segregation, but may impact performance if all dies/flash interface modules (FIMs) are not used in parallel.

The host device typically has substantial control over the data storage device. Typically, the host device selects the NVMe set/endurance group for zone creation (i.e., zone open and zone append). However, within a NVMe set/endurance group, the host device may not be aware of the workload on physical resources of the data storage device such as dies, flash channel(s), and other storage specific resources such as parity check engines and cache buffers.

Additionally, in a typical ZNS system, the data storage device may act upon the zone commands according to the submission queue, and may not be able to bias the zone commands according to the state of the data storage device itself. Biasing the zone commands according to the data storage device state may optimize resource utilization, thereby increasing the quality of service (QoS) of the system.

Thus, there is a need in the art to efficiently utilize the data storage device resources while maintaining the data segregation benefits of ZNS.

SUMMARY OF THE DISCLOSURE

The present disclosure generally relates to creating new zones in a data storage device in a manner that ensures substantially even workload of the memory device storage locations. When receiving a zone open command in a zone namespace (ZNS) system, rather than randomly selecting an unopen zone, zones may be categorized based upon storage location workload so that any new zone that is opened utilizes the least utilized storage location. In so doing, generally even workload of the memory device storage locations is achieved.

In one embodiment, a data storage device comprises: a memory device; and a controller coupled to the memory device, wherein the controller is configured to: receive a zone open command; and create a zone from a first physical block of the memory device, wherein the created zone corresponds to a physical block that has received the least workload in the memory device.

In another embodiment, a data storage device comprises: a memory device; and a controller coupled to the memory device, wherein the controller is configured to: evaluate a plurality of commands received in a submission queue; determine that a command of the plurality of commands is a zone open command; evaluate a backend of the memory device to determine a workload of available dies of the memory device; opening a new zone based upon the evaluation of the backend of the memory device; and route data associated with the zone open command to the new zone.

In another embodiment, a data storage device comprises: memory means; a controller coupled to the memory means, wherein the controller is configured to: receive a zone open command; determine multiple backend units of the memory means are eligible for a zone open and have a same amount of workload in the backend units; determine that a first backend unit of the multiple backend units has a lower number of program-erase cycles as compared to a remainder of the multiple backend units eligible; and open a new zone in the first backend unit.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

FIG. 1 is a schematic block diagram illustrating a storage system, according to one embodiment.

FIG. 2A illustrates zoned namespaces (ZNSs) utilized in a storage device, according to one embodiment.

FIG. 2B illustrates a state diagram for the ZNSs of the storage device of FIG. 2A, according to one embodiment.

FIG. 3 illustrates a NVMe set/endurance group in a ZNS system according to one embodiment.

FIG. 4 is a flowchart illustrating a FTL flow for dissimilar prioritization of writes into a zone according to one embodiment.

FIG. 5 is a flowchart illustrating a method of ensuring efficient wear leveling of a ZNS device.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.

DETAILED DESCRIPTION

In the following, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the disclosure. Furthermore, although embodiments of the disclosure may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the disclosure. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the disclosure” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).

The present disclosure generally relates to creating new zones in a data storage device in a manner that ensures substantially even workload of the memory device storage locations. When receiving a zone open command in a zone namespace (ZNS) system, rather than randomly selecting an unopen zone, zones may be categorized based upon storage location workload so that any new zone that is opened utilizes the least utilized storage location. In so doing, generally even workload of the memory device storage locations is achieved.

FIG. 1 is a schematic block diagram illustrating a storage system 100 in which data storage device 106 may function as a storage device for a host device 104, in accordance with one or more techniques of this disclosure. For instance, the host device 104 may utilize non-volatile memory 110 included in data storage device 106 to store and retrieve data. The host device 104 includes a host DRAM 138. In some examples, the storage system 100 may include a plurality of storage devices, such as the data storage device 106, which may operate as a storage array. For instance, the storage system 100 may include a plurality of data storages devices 106 configured as a redundant array of inexpensive/independent disks (RAID) that collectively function as a mass storage device for the host device 104.

The storage system 100 includes the host device 104 which may store and/or retrieve data to and/or from one or more storage devices, such as the data storage device 106. As illustrated in FIG. 1 , the host device 104 may communicate with the storage device 106 via an interface 114. The host device 104 may comprise any of a wide range of devices, including computer servers, network attached storage (NAS) units, desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called “smart” phones, so-called “smart” pads, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, and the like.

The data storage device 106 includes a controller 108, non-volatile memory (NVM) 110, a power supply 111, volatile memory 112, and an interface 114. The controller 108 comprises an internal memory 120 or buffer. In some examples, the data storage device 106 may include additional components not shown in FIG. 1 for sake of clarity. For example, the data storage device 106 may include a printed board (PB) to which components of the data storage device 106 are mechanically attached and which includes electrically conductive traces that electrically interconnect components of the data storage device 106, or the like. In some examples, the physical dimensions and connector configurations of the data storage device 106 may conform to one or more standard form factors. Some example standard form factors include, but are not limited to, 3.5″ data storage device (e.g., an HDD or SSD), 2.5″ data storage device, 1.8″ data storage device, peripheral component interconnect (PCI), PCI-extended (PCI-X), PCI Express (PCIe) (e.g., PCIe x1, x4, x8, x16, PCIe Mini Card, MiniPCI, etc.). In some examples, the data storage device 106 may be directly coupled (e.g., directly soldered) to a motherboard of the host device 104.

The interface 114 of the data storage device 106 may include one or both of a data bus for exchanging data with the host device 104 and a control bus for exchanging commands with the host device 104. The interface 114 may operate in accordance with any suitable protocol. For example, the interface 114 may operate in accordance with one or more of the following protocols: advanced technology attachment (ATA) (e.g., serial-ATA (SATA) and parallel-ATA (PATA)), Fibre Channel Protocol (FCP), small computer system interface (SCSI), serially attached SCSI (SAS), PCI, and PCIe, non-volatile memory express (NVMe), OpenCAPI, GenZ, Cache Coherent Interface Accelerator (CCIX), Open Channel SSD (OCSSD), or the like. The electrical connection of the interface 114 (e.g., the data bus, the control bus, or both) is electrically connected to the controller 108, providing electrical connection between the host device 104 and the controller 108, allowing data to be exchanged between the host device 104 and the controller 108. In some examples, the electrical connection of the interface 114 may also permit the data storage device 106 to receive power from the host device 104. For example, as illustrated in FIG. 1 , the power supply 111 may receive power from the host device 104 via the interface 114.

The data storage device 106 includes NVM 110, which may include a plurality of media units or memory devices. NVM 110 may be configured to store and/or retrieve data. For instance, a media unit of NVM 110 may receive data and a message from the controller 108 that instructs the memory device to store the data. Similarly, the media unit of NVM 110 may receive a message from the controller 108 that instructs the memory device to retrieve data. In some examples, each of the media units may be referred to as a die. In some examples, a single physical chip may include a plurality of dies (i.e., a plurality of memory devices). In some examples, each memory devices may be configured to store relatively large amounts of data (e.g., 128 MB, 256 MB, 512 MB, 1 GB, 2 GB, 4 GB, 8 GB, 16 GB, 32 GB, 64 GB, 128 GB, 256 GB, 512 GB, 1 TB, etc.).

In some examples, each media unit of NVM 110 may include any type of non-volatile memory devices, such as flash memory devices, phase-change memory (PCM) devices, resistive random-access memory (ReRAM) devices, magnetoresistive random-access memory (MRAM) devices, ferroelectric random-access memory (F-RAM), holographic memory devices, and any other type of non-volatile memory devices.

The NVM 110 may comprise a plurality of flash memory devices. Flash memory devices may include NAND or NOR based flash memory devices, and may store data based on a charge contained in a floating gate of a transistor for each flash memory cell. In NAND flash memory devices, the flash memory device may be divided into a plurality of blocks which may divided into a plurality of pages. Each block of the plurality of blocks within a particular memory device may include a plurality of NAND cells. Rows of NAND cells may be electrically connected using a word line to define a page of a plurality of pages. Respective cells in each of the plurality of pages may be electrically connected to respective bit lines. Furthermore, NAND flash memory devices may be 2D or 3D devices, and may be single level cell (SLC), multi-level cell (MLC), triple level cell (TLC), or quad level cell (QLC). The controller 108 may write data to and read data from NAND flash memory devices at the page level and erase data from NAND flash memory devices at the block level.

The data storage device 106 includes a power supply 111, which may provide power to one or more components of the data storage device 106. When operating in a standard mode, the power supply 111 may provide power to the one or more components using power provided by an external device, such as the host device 104. For instance, the power supply 111 may provide power to the one or more components using power received from the host device 104 via the interface 114. In some examples, the power supply 111 may include one or more power storage components configured to provide power to the one or more components when operating in a shutdown mode, such as where power ceases to be received from the external device. In this way, the power supply 111 may function as an onboard backup power source. Some examples of the one or more power storage components include, but are not limited to, capacitors, super capacitors, batteries, and the like. In some examples, the amount of power that may be stored by the one or more power storage components may be a function of the cost and/or the size (e.g., area/volume) of the one or more power storage components. In other words, as the amount of power stored by the one or more power storage components increases, the cost and/or the size of the one or more power storage components also increases.

The data storage device 106 also includes volatile memory 112, which may be used by controller 108 to store information. Volatile memory 112 may be comprised of one or more volatile memory devices. In some examples, the controller 108 may use volatile memory 112 as a cache. For instance, the controller 108 may store cached information in volatile memory 112 until cached information is written to non-volatile memory 110. As illustrated in FIG. 1 , volatile memory 112 may consume power received from the power supply 111. Examples of volatile memory 112 include, but are not limited to, random-access memory (RAM), dynamic random access memory (DRAM), static RAM (SRAM), and synchronous dynamic RAM (SDRAM (e.g., DDR1, DDR2, DDR3, DDR3L, LPDDR3, DDR4, LPDDR4, and the like)).

The data storage device 106 includes a controller 108, which may manage one or more operations of the data storage device 106. For instance, the controller 108 may manage the reading of data from and/or the writing of data to the NVM 110. In some embodiments, when the data storage device 106 receives a write command from the host device 104, the controller 108 may initiate a data storage command to store data to the NVM 110 and monitor the progress of the data storage command. The controller 108 may determine at least one operational characteristic of the storage system 100 and store the at least one operational characteristic to the NVM 110. In some embodiments, when the data storage device 106 receives a write command from the host device 104, the controller 108 temporarily stores the data associated with the write command in the internal memory 120 before sending the data to the NVM 110.

FIG. 2A illustrates zoned namespace (ZNS) 202 view utilized in a storage device 200, according to one embodiment. The storage device 200 may present the ZNS 202 view to a host device. FIG. 2B illustrates a state diagram 250 for the ZNS 202 of the storage device 200, according to one embodiment. The storage device 200 may be the data storage device 106 of the storage system 100 of FIG. 1 . The storage device 200 may have one or more ZNS 202, and each ZNS 202 may be different sizes. The storage device 200 may further comprise one or more conventional namespaces in addition to the one or more ZNS 202. Moreover, the ZNS 202 may be a zoned block command (ZBC) for SAS and/or a zoned-device ATA command set (ZAC) for SATA.

In the storage device 200, the ZNS 202 is the quantity of NVM that can be formatted into logical blocks such that the capacity is divided into a plurality of zones 206 a-206 n (collectively referred to as zones 206). Each of the zones 206 comprise a plurality of physical or erase blocks (now shown) of a media unit or NVM 204, and each of the erase blocks are associated a plurality of logical blocks (not shown). When the controller 208 receives a command, such as from a host device (not shown) or the submission queue of a host device, the controller 208 can read data from and write data to the plurality of logical blocks associated with the plurality of erase blocks of the ZNS 202. Each of the logical blocks is associated with a unique LBA or sector.

In one embodiment, the NVM 204 is a NAND device. The NAND device comprises one or more dies. Each of the one or more dies comprises one or more planes. Each of the one or more planes comprises one or more erase blocks. Each of the one or more erase blocks comprises one or more wordlines (e.g., 256 wordlines). Each of the one or more wordlines may be addressed in one or more pages. For example, an MLC NAND die may use an upper page and a lower page to reach the two bits in each cell of the full wordline (e.g., 16 kB per page). Furthermore, each page can be accessed at a granularity equal to or smaller than the full page. A controller can frequently access NAND in user data granularity LBA sizes of 512 bytes. Thus, as referred to in the below description, NAND locations are equal to a granularity of 512 bytes. As such, an LBA size of 512 bytes and a page size of 16 kB for two pages of an MCL NAND results in about 16 NAND locations per wordline. However, the NAND location size is not intended to be limiting, and is merely used as an example.

When data is written to an erase block, one or more logical blocks are correspondingly updated within a zone 206 to track where the data is located within the NVM 204. Data may be written to one zone 206 at a time until a zone 206 is full, or to multiple zones 206 such that multiple zones 206 may be partially full. Similarly, when writing data to a particular zone 206, data may be written to the plurality of erase blocks one block at a time, in sequential order of NAND locations, page-by-page, or wordline-by-wordline, until moving to an adjacent block (i.e., write to a first erase block until the first erase block is full before moving to the second erase block), or to multiple blocks at once, in sequential order of NAND locations, page-by-page, or wordline-by-wordline, to partially fill each block in a more parallel fashion (i.e., writing the first NAND location or page of each erase block before writing to the second NAND location or page of each erase block).

Each of the zones 206 is associated with a zone starting logical block address (ZSLBA). The ZSLBA is the first available LBA in the zone 206. For example, the first zone 206 a is associated with Z_(a)SLBA, the second zone 206 b is associated with Z_(b)SLBA, the third zone 206 c is associated with Z_(c)SLBA, the fourth zone 206 d is associated with Z_(d)SLBA, and the n^(th) zone 206 n (i.e., the last zone) is associated with Z_(n)SLBA. Each zone 206 is identified by its ZSLBA, and is configured to receive sequential writes (i.e., writing data to the NVM 110 in the order the write commands are received).

As data is written to a zone 206, a write pointer 210 is advanced or updated to point to or to indicate the next available block in the zone 206 to write data to in order to track the next write starting point (i.e., the completion point of the prior write equals the starting point of a subsequent write). Thus, the write pointer 210 indicates where the subsequent write to the zone 206 will begin. Subsequent write commands are ‘zone append’ commands, where the data associated with the subsequent write command appends to the zone 206 at the location the write pointer 210 is indicating as the next starting point. An ordered list of LBAs within the zone 206 may be stored for write ordering. Each zone 206 may have its own write pointer 210. Thus, when a write command is received, a zone is identified by its ZSLBA, and the write pointer 210 determines where the write of the data begins within the identified zone.

FIG. 2B illustrates a state diagram 250 for the ZNS 202 of FIG. 2A. In the state diagram 250, each zone may be in a different state, such as empty, active, full, or offline. When a zone is empty, the zone is free of data (i.e., none of the erase blocks in the zone are currently storing data) and the write pointer is at the ZSLBA (i.e., WP=0). An empty zone switches to an open and active zone once a write is scheduled to the zone or if a zone open command is issued by the host. Zone management (ZM) commands can be used to move a zone between zone open and zone closed states, which are both active states. If a zone is active, the zone comprises open blocks that may be written to, and the host may be provided a description of recommended time in the active state. The controller may comprise the ZM.

The term “written to” includes programming user data on 0 or more word lines in an erase block, erasure, and/or partially filled word lines in an erase block when user data has not filled all of the available word lines. The term “written to” may further include closing a zone due to internal drive handling needs (open block data retention concerns because the bits in error accumulate more quickly on open erase blocks), the storage device 200 closing a zone due to resource constraints, like too many open zones to track or discovered defect state, among others, or a host device closing the zone for concerns such as there being no more data to send the drive, computer shutdown, error handling on the host, limited host resources for tracking, among others.

The active zones may be either open or closed. An open zone is an empty or partially full zone that is ready to be written to and has resources currently allocated. The data received from the host device with a write command or zone append command may be programmed to an open erase block that is not currently filled with prior data. New data pulled-in from the host device or valid data being relocated may be written to an open zone. Valid data may be moved from one zone (e.g. the first zone 202 a) to another zone (e.g. the third zone 202 c) for garbage collection purposes. A closed zone is an empty or partially full zone that is not currently receiving writes from the host in an ongoing basis. The movement of a zone from an open state to a closed state allows the controller 208 to reallocate resources to other tasks. These tasks may include, but are not limited to, other zones that are open, other conventional non-zone regions, or other controller needs.

In both the open and closed zones, the write pointer is pointing to a place in the zone somewhere between the ZSLBA and the end of the last LBA of the zone (i.e., WP>0). Active zones may switch between the open and closed states per designation by the ZM, or if a write is scheduled to the zone. Additionally, the ZM may reset an active zone to clear or erase the data stored in the zone such that the zone switches back to an empty zone. Once an active zone is full, the zone switches to the full state. A full zone is one that is completely filled with data, and has no more available blocks to write data to (i.e., WP=zone capacity (ZCAP)). Read commands of data stored in full zones may still be executed.

The ZM may reset a full zone, scheduling an erasure of the data stored in the zone such that the zone switches back to an empty zone. When a full zone is reset, the zone may not be immediately cleared of data, though the zone may be marked as an empty zone ready to be written to. However, the reset zone must be erased prior to switching to an active zone. A zone may be erased any time between a ZM reset and a ZM open. An offline zone is a zone that is unavailable to write data to. An offline zone may be in the full state, the empty state, or in a partially full state without being active.

Since resetting a zone clears or schedules an erasure of the data stored in the zone, the need for garbage collection of individual erase blocks is eliminated, improving the overall garbage collection process of the storage device 200. The storage device 200 may mark one or more erase blocks for erasure. When a new zone is going to be formed and the storage device 200 anticipates a ZM open, the one or more erase blocks marked for erasure may then be erased. The storage device 200 may further decide and create the physical backing of the zone upon erase of the erase blocks. Thus, once the new zone is opened and erase blocks are being selected to form the zone, the erase blocks will have been erased. Moreover, each time a zone is reset, a new order for the LBAs and the write pointer 210 for the zone 206 may be selected, enabling the zone 206 to be tolerant to receive commands out of sequential order. The write pointer 210 may optionally be turned off such that a command may be written to whatever starting LBA is indicated for the command.

Referring back to FIG. 2A, when the controller 208 initiates or pulls-in a write command, the controller 208 may select an empty zone 206 to write the data associated with the command to, and the empty zone 206 switches to an active zone 206. As used herein, the controller 208 initiating or pulling-in a write command comprises receiving a write command or direct memory access (DMA) reading the write command. The write command may be a command to write new data, or a command to move valid data to another zone for garbage collection purposes. The controller 208 is configured to DMA read or pull-in new commands from a submission queue populated by a host device.

In an empty zone 206 just switched to an active zone 206, the data is written to the zone 206 starting at the ZSLBA, as the write pointer 210 is indicating the logical block associated with the ZSLBA as the first available logical block. The data may be written to one or more erase blocks or NAND locations that have been allocated for the physical location of the zone 206. After the data associated with the write command has been written to the zone 206, the write pointer 210 is updated to point to the next available block in the zone 206 to track the next write starting point (i.e., the completion point of the first write). Alternatively, the controller 208 may select an active zone to write the data to. In an active zone, the data is written to the logical block indicated by the write pointer 210 as the next available block.

In some embodiments, a NAND location may be equal to a wordline. In such an embodiment, if the write command is smaller than a wordline, the controller may optionally aggregate several write commands in another memory location such as DRAM or SRAM prior to programming a full wordline composed of multiple write commands. Write commands that are longer than a wordline will be able to program and fill a complete wordline with some of the data, and the excess data beyond a wordline will be used to fill the next wordline. However, a NAND location is not limited to being equal to a wordline, and may have a larger or smaller size than a wordline. For example, in some embodiments, a NAND location may be equal to the size of a page.

For example, the controller 208 may receive, pull-in, or DMA read a first write command to a third zone 206 c, or a first zone append command. The host identifies sequentially which logical block of the zone 206 to write the data associated with the first command to. The data associated with the first command is then written to the first or next available LBA(s) in the third zone 206 c as indicated by the write pointer 210, and the write pointer 210 is advanced or updated to point to the next available LBA available for a host write (i.e., WP>0). If the controller 208 receives or pulls-in a second write command to the third zone 206 c, the data associated with the second write command is written to the next available LBA(s) in the third zone 206 c identified by the write pointer 210. Once the data associated with the second command is written to the third zone 206 c, the write pointer 210 once again advances or updates to point to the next available LBA available for a host write. Resetting the third zone 206 c moves the write pointer 210 back to the Z_(c)SLBA (i.e., WP=0), and the third zone 406 c switches to an empty zone.

FIG. 3 illustrates a NVMe set/endurance group in a ZNS system according to one embodiment. As shown in FIG. 3 , a plurality of applications 302 a-302 c connect to the data storage device firmware 304 through respective flash transition layers (FTLs) to access the memory devices 306 a-306 c that each comprise a plurality of dies 308. In operation, each application, which could be different hosts of virtual hosts, has access to the same data storage device 310 and hence, memory devices 306 a-306 c and dies 308. The zones for a ZNS device can be set up across the dies 308 or within any die 308.

In ZNS, a zone open command occurs when the first write triggers the logic that allocates a new zone. The zone write occurs when the start LBA (SLBA) is equal to the zone start LBA (ZSLBA). Similarly, a zone append/write command is where the SLBA does not equal ZSLBA such that the writes are added to an already opened zone.

It is to be understood that backend units include physical blocks in the ZNS NVMe set/endurance group. In general, a ZNS device looks for zone append and zone read commands in a submission queue and prioritizes those commands to the backend without any conditions. However, for zone open commands, the zones are created using backend units that are not currently in use by other zones. If those zones are created randomly or utilizing the same dies over time, then the dies do not receive an even workload and hence, the ZNS device has uneven workload, impacting QoS. It is desirable to create a zone where the workload in terms of die/FIM is least utilized so that each time a new zone is created, the zone utilizes the least utilized die/FIM so that the device has an even workload and even wear over time. The intention is to make the zone open command use the leftover backend resources due to non-dependency on exact hardware (HW). In other words, the disclosure involves dissimilar prioritization for writes into zones based on the zone offset. The controller utilizes the non-attachment of the device resources until the zone start for writing. Subsequently, the zone mapping is updated for the new zone with allocated physical blocks as in a typical ZNS system.

The zone append and zone read commands are non-negotiable candidates in terms of a particular resource workload. That is, when a zone read is issued, the zone read can only be read from the particular die/FIM (physical block in that ZNS NVMe set/endurance group) where the data is written. Similarly, for a zone append, the zone can be appended to only that particular zone where the write was previously started (already open physical block is in use).

Zone open commands, on the other hand, are cases where the ZNS hosts wants to write data from zero zone offset (zone create to start with) to the device, and the host does not care where those data physically reside, as long as the zone is part of the NVMe set/endurance group and that the zone to physical (Z2P) mapping is intact. The ZNS controller can leverage the condition.

On receiving a zone open request, zones can be created out of physical blocks in that part of the backend in the ZNS NVMe set/endurance group, where the die/FIM has the least workload. The host data and zone open request can be routed to create such zones, which results in better HW utilization, which in turn leads to optimum quality of service (QoS) of the ZNS product. Since the zone read commands and zone append commands are prioritized ahead of the zone open command, the non-negotiable resources are already triggered, on priority, for workload in the device. Hence, the method ensures that the zone open minimally interferes with HW resources required for the zone append and zone read commands. The zone open command aims to use the leftover resources due to non-dependency on exact HW.

FIG. 4 is a flowchart 400 illustrating a FTL flow for dissimilar prioritization of writes into a zone according to one embodiment. As shown in FIG. 4 , commands are initially placed in a submission queue by a host device. The data storage device then evaluates the commands in the submission queue at 402 looking to see whether the commands within the submission queue are zone read commands, zone append commands or zone open commands. The data storage device, and more particularly the controller, sorts through the submission queue to sort the commands and to make a determination at 404 whether the commands are zone append, zone read, or zone open commands. The zone append and zone read commands are given a high priority for moving to the backend of the data storage device for execution. The zone read commands are sent to the backend for execution at 406 while the zone append commands are send to the backend for execution at 408. After sending the zone read and zone append commands to the backend, the controller then deals with the zone open commands.

The controller performs a zone open at 410 in the backend unit of the ZNS NVMe set/endurance group. The zone open is performed to open a zone where the workload is a minimum in terms of die, FIM, cache, and/or error correction engine workload. The new zone will leverage the maximum out of the freely available HW resources because the zone read and zone append commands are prioritized ahead of the zone open command.

The workload of the storage backend unit (i.e., die/FIM) in any ZNS NVMe set is associated with a credit point according to the read/write activity, and a moving window to decide on a zone open at any point in time. Any known methods, either firmware (FW) or HW may be employed by the data storage device to evaluate such workloads. Counter based FW methods for different resources is one example. Stated another way, wear leveling schemes may be accommodated during the process wherein if the controller determines that multiple backend units are eligible for zone open in terms of least workload, the unit offering the physical block with a lower program-erase count may be the winner for selection as the new zone to open. Over a long run, such a strategy will provide better sustained mixed load performance as well as better wear leveling. The same logic is applicable to read scrub operations, failure management, and other storage backend management techniques. The controller chooses a destination block in the backend unit of a NVMe set of a ZNS device which has the least workload for HW and lower program-erase block attached to that set. The controller does the selection after all the host issued ZNS appends and ZNS reads are prioritized.

In one embodiment, a program-erase parameter is used to determine which zone to open. The program-erase parameter is used when there is a ‘tie’ in terms of workload such that there are multiple zones that could be open that have the same workload history in terms of die, FIM, cache, and/or error correction engine workload. In so doing, the zone with the fewest program-erase cycles is chosen. Thus, wear leveling across the blocks is achieved.

The controller then updates the zone to logical (Z2L) mapping at 412. Finally, the host's zone open command data is routed to the newly created zone at 414. The cycle then ends at 416.

As noted above, uneven wear in a data storage device can be an issue. Wear leveling ensures efficient use of the device, longer device lifetime, and good QoS. As discussed herein, for a ZNS device, a way to ensure wear leveling is processing a zone open command to open zones that have the least utilized memory devices. The zone open command differs from the zone read command and the zone append command. Both the zone read command and the zone append command are commands that are performed on already opened zones. Already opened zones have memory devices or areas of memory devices that are already allocated thereto. New zones, on the other hand, can be created from memory devices or areas of memory devices that are not currently in allocated to a zone. The devices or areas not currently allocated to a zone can be evaluated to determine which devices or areas have the least amount of workload history. New zones can be created from the areas or devices that have the least amount of workload history. Number of program-erase cycles can be used as a tiebreaker for any areas or devices that have the same amount of workload history.

FIG. 5 is a flowchart 500 illustrating a method of ensuring efficient wear leveling of a ZNS device. At 502, a host device rings a doorbell to inform the data storage device that there are commands in a submission queue that need processing. The data storage device then retrieves the commands and sorts the commands at 504. Any zone read commands or zone append commands are immediately forwarded to the backend of the data storage device for immediate processing and 506. As the zone read commands or zone append commands are completed, a completion queue of the host is filled and a doorbell is rung to inform the host that the completion queue has information therein.

Now that the zone append and zone read commands have been sent to the backend, any zone open commands from the submission queue may be processed. To process the zone open commands, a new zone needs to be created. Creating a zone involves assessing the available memory devices and areas of the memory devices (in cases where a memory device can have different data locations or blocks that can be allocated to different zones) for workload history at 508. After determining the devices and/or areas with the lowest workload history, the controller determines if there are any ties at 510. If there are no ties, then the zone can be opened at 512. If there are ties, then the controller settles the ties by ranking the tied devices and/or areas based upon program-erase cycle history at 514. The devices and/or areas with the fewest program-erase cycles is selected are chosen as the devices and/or areas with the lowest workload at 516 and then opens the zone. Once the zone is opened, the data associated with the zone open command is then written to the newly opened zone at 518. Once the data is written, an entry is made in the completion queue, and the doorbell is rung to inform the host of an entry in the completion queue at 520.

By purposefully selecting the least utilized memory devices and/or memory areas for processing zone open commands, even device wear leveling is achieved. Even device wear leveling ensures efficient use of the device, longer device lifetime, and good QoS.

In one embodiment, a data storage device comprises: a memory device; and a controller coupled to the memory device, wherein the controller is configured to: receive a zone open command; and create a zone from a first physical block of the memory device, wherein the created zone corresponds to a physical block that has received the least workload in the memory device. The controller is further configured to receive a plurality of zone commands, wherein at least one of the plurality of zone commands is the zone open command. At least a first command of the plurality of commands is a zone read command, wherein the controller is further configured to process the zone read command prior to the zone open command. At least a first command of the plurality of commands is a zone append command, wherein the controller is further configured to process the zone append command prior to the zone open command. The workload is based upon amount of read and write activity for the physical block. The zone open command is processed after any zone append or zone read commands have begun executing. The least workload is based upon die workload, flash interface module (FIM) workload, cache workload, and/or parity check engine workload. The controller is configured to determine a plurality of physical blocks have the least workload, wherein the first physical block has a lower number of program-erase cycles as compared to a remainder of the plurality of physical blocks. The controller is further configured to maintain wear leveling across physical blocks of the memory device. The zone open command is received in a submission queue, and wherein the controller is configured to process any zone append commands or zone read commands prior to the zone open command.

In another embodiment, a data storage device comprises: a memory device; and a controller coupled to the memory device, wherein the controller is configured to: evaluate a plurality of commands received in a submission queue; determine that a command of the plurality of commands is a zone open command; evaluate a backend of the memory device to determine a workload of available dies of the memory device; opening a new zone based upon the evaluation of the backend of the memory device; and route data associated with the zone open command to the new zone. The controller is further configured to update a zone to logical block address table after opening the new zone. The controller is further configured to route zone read commands and zone append commands to the backend prior to opening the new zone. The evaluation occurs at a flash translation layer (FTL). The zone open command is a zone command with zero offset.

In another embodiment, a data storage device comprises: memory means; a controller coupled to the memory means, wherein the controller is configured to: receive a zone open command; determine multiple backend units of the memory means are eligible for a zone open and have a same amount of workload in the backend units; determine that a first backend unit of the multiple backend units has a lower number of program-erase cycles as compared to a remainder of the multiple backend units eligible; and open a new zone in the first backend unit. The controller is further configured to direct zone append commands to a second backend unit that is distinct from the first backend unit. The controller is further configured to direct zone read commands to a third backend unit that is distinct from the first backend unit. The controller is further configured to direct the zone append commands and the zone read commands to the second backend unit and the third backend unit respectively prior to determining multiple backend units of the memory means are eligible. The controller is further configured to search a submission queue to find the zone open command and any zone append command or any zone read command.

While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

1. A data storage device, comprising: a memory device; and a controller coupled to the memory device, wherein the controller is configured to: receive a zone open command; determine that a tie exists in terms of workload between a first physical block and another physical block, rank the first physical block and the another physical block based upon a number of program-erase cycles, wherein the first physical block has a fewer number of program-erase cycles; and create a zone from the first physical block of the memory device, wherein the created zone corresponds to a physical block that has received the least workload in the memory device.
 2. The data storage device of claim 1, wherein the controller is further configured to receive a plurality of zone commands, wherein at least one of the plurality of zone commands is the zone open command.
 3. The data storage device of claim 2, wherein at least a first command of the plurality of commands is a zone read command, wherein the controller is further configured to process the zone read command prior to the zone open command.
 4. A data storage device, comprising: a memory device; and a controller coupled to the memory device, wherein the controller is configured to: receive a zone open command; and create a zone from a first physical block of the memory device, wherein the created zone corresponds to a physical block that has received the least workload in the memory device, wherein the controller is further configured to receive a plurality of zone commands, wherein at least one of the plurality of zone commands is the zone open command, wherein at least a first command of the plurality of commands is a zone append command, wherein the controller is further configured to process the zone append command prior to the zone open command.
 5. The data storage device of claim 1, wherein the workload is based upon amount of read and write activity for the physical block.
 6. The data storage device of claim 1, wherein the zone open command is processed after any zone append or zone read commands have begun executing.
 7. The data storage device of claim 1, wherein the least workload is based upon die workload, flash interface module (FIM) workload, cache workload, and/or parity check engine workload.
 8. The data storage device of claim 1, wherein the controller is configured to determine a plurality of physical blocks have the least workload, wherein the first physical block has a lower number of program-erase cycles as compared to a remainder of the plurality of physical blocks.
 9. The data storage device of claim 1, wherein the controller is further configured to maintain wear leveling across physical blocks of the memory device.
 10. The data storage device of claim 1, wherein the zone open command is received in a submission queue, and wherein the controller is configured to process any zone append commands or zone read commands prior to the zone open command.
 11. A data storage device, comprising: a memory device; and a controller coupled to the memory device, wherein the controller is configured to: evaluate a plurality of commands received in a submission queue; determine that a command of the plurality of commands is a zone open command; evaluate a backend of the memory device to determine a workload of available dies of the memory device; opening a new zone based upon the evaluation of the backend of the memory device; and route data associated with the zone open command to the new zone.
 12. The data storage device of claim 11, wherein the controller is further configured to update a zone to logical block address table after opening the new zone.
 13. The data storage device of claim 11, wherein the controller is further configured to route zone read commands and zone append commands to the backend prior to opening the new zone.
 14. The data storage device of claim 11, wherein the evaluation occurs at a flash translation layer (FTL).
 15. The data storage device of claim 11, wherein the zone open command is a zone command with zero offset.
 16. A data storage device, comprising: memory means; a controller coupled to the memory means, wherein the controller is configured to: receive a zone open command; determine multiple backend units of the memory means are eligible for a zone open and have a same amount of workload in the backend units; determine that a first backend unit of the multiple backend units has a lower number of program-erase cycles as compared to a remainder of the multiple backend units eligible; and open a new zone in the first backend unit.
 17. The data storage device of claim 16, wherein the controller is further configured to direct zone append commands to a second backend unit that is distinct from the first backend unit.
 18. The data storage device of claim 17, wherein the controller is further configured to direct zone read commands to a third backend unit that is distinct from the first backend unit.
 19. The data storage device of claim 18, wherein the controller is further configured to direct the zone append commands and the zone read commands to the second backend unit and the third backend unit respectively prior to determining multiple backend units of the memory means are eligible.
 20. The data storage device of claim 16, wherein the controller is further configured to search a submission queue to find the zone open command and any zone append command or any zone read command. 